Civilian and military radio systems can be implemented on different platforms to perform diverse communication functions. Platforms can include backpacks, satellites, vehicles, naval vessels, aircraft, shelters, or other structures. Radio systems can even be hand-held systems. The diverse communication functions can involve the reception and the transmission of voice, data, or both by computer equipment or by personnel.
Radio systems operate in various modes, including voice and data modes, and transmit information in a number of frequency bands (L band, S band, C band, X band, VHF band, UHF band, HF band, and other frequency bands). Often, multiple users (personnel or equipment) on a single platform can simultaneously require radio services. The radio services can involve simplex and duplex communications in the various modes and on the various bands. For example, on an aircraft platform, a radio operator could be participating in a voice communication in the VHF band on one radio unit while navigational equipment communicates data in the L band via another radio unit. Thus, platforms can require simultaneous use of radio services in multiple modes and in multiple bands.
Heretofore, simultaneous independent radio operations have generally required separate, distinct radio units. Additionally, the distinct radio units are generally configured for use in a single mode and in a single band. Separate radio units for each user, mode, and band add to the cost of providing radio services on the platform. Further, separate radio units add to the power requirements and to the weight of the platform.
Conventional radio systems, especially co-spectrum frequency hopping systems, do not have high quality reception at the necessary receiver sensitivity levels for simultaneous operations. The high quality reception problem can be due to the high level transmit noise floor compared to the sensitivity level of the receiver. Also, the high quality reception problem can be due to high levels of transmitted intermodulation, harmonic, and spurious distortion which cause the automatic gain control of the receiver to reduce the gain and, thereby, degrade the sensitivity level. Additionally, the high quality reception problem can be due to concurrent high/low signal reception levels (e.g., the near/far reception problem). The near/far reception problem can cause the gain of the receiver to be reduced for the high level signal, thereby burying the low level signal in receiver noise.
Conventional radio systems have relied on analog designs that include analog intermediate frequency (IF) circuits and analog modulation and demodulation circuits. The analog designs are configured for single user, single mode, and single band operations and generally do not allow programmability or flexibility for multi-mode, multi-band, and multi-user radio services.
To the extent conventional radio systems include digital base band circuitry, analog IF circuitry is still required to convert the base band signal to/from a radio frequency (RF) band and to perform gain control functions. Further, the conversion band width of these conventional systems is fairly narrow and is usually below 10 megahertz (MHz).
Thus, there is a need for a radio system architecture that supports high dynamic range in multiple bands and simultaneous operation. Further, there is a need for a radio system which is multi-band, multi-mode, and multi-user. Even further still, there is a need for a radio system which includes a direct sampling receiver (DSR) and a direct digital transmitter (DDT) architecture.